The fact that the DFT dilaton \(e^{-2d}\)  carries a nontrivial diffeomorphic weight prevents it from coupling to the \(\mathbf {O}(D,D)\) -symmetric doubled-yet-gauged particle and string actions [1]}, [2]}, [3]}. This rigidity naturally settles the issue of the frame ambiguity: upon the Riemannian background of (REF ), an \(\mathbf {O}(D,D)\) -symmetric particle follows geodesics defined in the string frame [4]}.
